Turntable drive system



Oct. 25, 1949. T. c. SHARP TURNTABLE DRIVE SYSTEI 2 Sheds-Sheet 1 Filed FQb. 12, 1947 mmuu 'IIIHII llllllllilllllll'll 17914517705. I 77/0/14: CQSA MP irrozvi/ Oct. 25, 1949. T. c. SHARP TURNTABLE DRIVE SYSTEM 2 Sheets-Sheet 2 Filed Feb. 12, 1947 mi l l- .f/vvmraz. 77mm 6, J/hzp 1 W1. W

Ame/v 1 Patented Oct- 25, 1949 UNITED STATES PATENT OFFICE 2,485, 8

, TURNTABLE DRIVE 8Y8!!! Thomas-C. Sharp, North Hollywood. Calif., assignortonadiocomntlonoflimerlmaoorporation of Delaware Application Febrnm 12. 184%. Serial No. new

4 Claims. (0. 318-84) 2 fore, is to facilitate the obtaining of a constant and uniform speed for a sound record.

Another object of the invention is to provide an improved method of and motor drive for a This invention relates to motor drives and particularly to a motor drive system for a record supporting. turntable which may be used for either recording or reproducing sound.-

In the art of phonograph sound recording and g phonograph turntable, reproduction wherein the disc type of record is A further object of the invention is to provide employed, the record supporting table or turnan improved motor drive between a motor and table is generally driven at either of two standa turntable driven thereby which obviates the ard speeds, such as 33% or 78 revolutions per necessity of a gear rotating at turntable speed. minute. The turntable is usually driven by a A still further object of the invention is to motor through a shaft and set of reduction gears. provide a turntable driving system which utilizes A turntable drive of this type is disclosed and a magnetic field coupling between a high speed claimed in Carson et al. U. S. Patent No. 2,106,718 rotating element and a low speed rotating eleof February 1, 1938. ment. It is well known that it is desirable to have A still further object of the invention is to prothe turntable rotate at a constant and uniform vide an improved filter for a sound record turnspeed in order to eliminate distortion, variations table. in speed changing the frequency of the sound be- Although the novel features which are believed this invention will be to be characteristic of pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanyin drawings forming a part hereof, in which:

Fig. 1 is an elevational view partially in cross section of a motor drive embodying the invention.

Fig. 2 is a cross ing recorded and reproduced. Various methods of and means for obtaining a substantially constant speed have been suggested and employed, these prior methods using fly wheels and medamped filters of different forms. filter is disclosed and claimed S. Patent No. 2,133,390 of April One of the chief difllculties in obtaining a uniform speed of rotation of the turntable is in the use of the gears required for reducing the speed sectional view of a portion of of the motor, which usually rotates in'the neighm Fig. 1 and a turntable filter, and borhood of 1,200 to 1,800 revolutions per min- 3 is a plan view of the turntable filter ute, to the speed of the turntable which is either taken along the line of 3-3 of Fig.

Referring now to the drawings in which the same numerals identify like elements, a salient pole or slip ring motor 5 rotates a shaft 0 having a gear 1 mountedthereon. In mesh with gear I is a gear ll mounted on a shaft H which drives a squirrel cage rotor ll of a second salient pole motor ll having 'a stator winding I! (see 33% or '18 revolutions per minute. It has been found almost impossible to maintain gears 'between motor and turntable in such a condition that a once around" variation in the speed of the turntable is not introduced. These speed variations produce what are commonly known as wows, and are traceable to the fact thatthereis at least one gear rotating at the same speed so Fig. 2). The stator mounted in the housing as the turntable. it is adapted to be rotated on bearings 2. and The present invention is directed to a motor 2i while the rotor II is rotatable on bearings drive system fora record turntable which, al- 22 and it.

though gears may be used in a certain portion Directly connected to the upper end bell ll of the drive, they are rotated at a much higher of the housing It is a shaft 26 connected to a speed than the turntable speed, the reduction peed being accomplished by the magnetic field differential between a driven rotor and an energized stator of an intermediate motor. In the new drive, the coupling between the high s eed unit and the low speed unit is magnetic I and therefore is not subject to the mechanical imperfections of gears. Furthermore, 'any imperfections in the high speedgears are filtered out by the intermediate magnetic coupling. However, if any speed disturbances should be extraneously introduced a novel turntable filter may be added although the filter may be used with the standard type of drive.

The principal object of shaft 21 through a coupling 28. As shown in Fig. 1 the shaft 2! drives a turntable ll mounted on a pair of bearings 3|. The stator windings ii are connected through three slip rings 34 to any suitable three phase power supply.

In operation the motor 5 is energized for rotation at any suitable speed such as ,800 revolutions per minute. The gears 'l and 10 are then chosen so that the rotation of the rotor II is at a speed of 1.766% revolutions per minute. Assuming that the normal speed of the stator ii would be 1,800 revolutions per minute if the rotor 13 were stationary, the actual speed at which the stator actually rotates when the rotor is 60 driven at 1.766% revolutions per minute is the the invention, theredifference between 1,800 and 66%, or 38% revolutions per minute. By changing the ratio of the gears 1 and III the rotor would rotate at a speed 01' 1,722 revolutions per minute, and a turntable speed of 78 revolutions per minute would result. Other speeds could be easily obtained with standard speed motors by simply providing the proper gear ratio.

Although gears are actually used to couple motor to rotor l3 these gears are rotating at a much higher speed of rotation than that of the turntable and any once around" variations in the gears would not be reflected in the turntable speed. The driving unit rotating at the speed of the turntable, namely, the stator I5, is magnetically and thus elastically coupled to the high speed unit, namely, the rotor l3. A filter is thereby formed the stator mass doing the damping. Such a drive has been found to provide a particularly constant speed even with the use of standard commercial gears purchased in the open market. The use of rotating stators for speed variations is known and disclosed in Fick U. S. Patent No. 1,527,637, the present invention, however, utilizing filter element in a reduction coupling.

I1 it is desired to obtain additional filtering action between the shaft 2'! and turntable 30 a novel turntable filter is illustrated in Figs. 2 and 3, it being understood, of course, that the turntable filter may also be used with the standard motor drive system to minimize the wows therefrom.

Referring now to Figs. 2 and 3, the fiat top of a turntable 31 has depending therefrom and attached to a central collar 39, a plurality of radial fins or vanes 38 with permanent magnet insert elements 40 positioned substantially half way along their length as shown in Fig. 3. The turntable is mounted on a single thrust bearing 42 and on a lateral stabilizing bearing 43. Interposed between the fins or vanes 38 are a group of similar fins or vanes 45 extending upwardly from the bottom surface of and attached to the outer rim of a driving element 46. Positioned along the length of the fins 45 at the same radial distance from the axis of rotation of the table as the element 40, are a plurality of permanent magnets 48 similar to magnets 40 on the vanes 38. The element 46 is adapted to contain all or a similar viscous damping material. As shown in Fig. 3, the magnets 40 and 48 are so poled that the north and south poles oppose one another and thus a resilient magnetic coupling is produced between the driving element 46 and the driven turntable 31. The oil between the vanes 38 and 45 introduces damping while the magnetic coupling provides the elastic component of the filter.

Thus, by the use of the motor field magnetic coupling in series with the magnetic coupling between the elements of the turntable, a very constant and uniform speed of rotation is obtainable for the turntable itself. As mentioned above, the gear wows in any standard gear driven motor drive will be greatly reduced by the use 01' the turntable magnetic filter shown in Figs. 2 and 3.

Iclaim:

1. A motor drive comprising a substantially independent constant speed motor unit, a stator and a rotor for said unit, a turntable adapted to be driven at a constant speed, an intermediate the magnetic coupling as a 40 connected to the stator of said second motor, and

011 between said fixed magnets.

4. A turntable driving system comprising a motor having a stationary stator and a rotatable rotor adapted to rotate at a comparativel high 4.; speed, a second motor having a rotatable rotor 50 eluding a vaned driving element connected to lug element vanes, said interposed vanes having magnets thereon opposing said first mentioned magnets, and 011 between said vanes.

THOMAS C. SHARP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number France Feb. 18, 1930 

